Unit 3 Optics Suggested Time: 26 Hours

Transcription

1 Unit 3 Optics Suggested Time: 26 Hours

2 Unit Overview Introduction Applications using the principles of light have resulted in devices that have improved scientific techniques and contributed to our quality of life. In this unit of study, basic concepts that are introduced include the properties of visible light including the reflection and refraction of light. Various reflecting and refracting technologies will also be explored and investigated. Students should be given opportunities to experience and observe the properties of light using hands-on activities. Opportunities and activities designed to investigate and explore the properties of light would provide the basis for more in-depth experimentation with materials in order to investigate reflection and refraction of light. Focus and Context Science Curriculum Links The focus of this unit is inquiry. A possible context could be the variety of everyday experiences the students have with the reflection and refraction of light. Students encounter reflection when they get up in the morning and use a mirror, for example. Buses and cars have a variety of reflective devices that could be explored. Eyeglasses and other refracting technologies could be investigated. In addition, students should have ample opportunity to investigate and study various technologies that are associated with electromagnetic radiation and to explore their positive and negative attributes and their impact on our way of life. In elementary grades, students began their formal investigation and study of light. Sources of light and how light travels are topics explored. As well, students investigated how white light can be separated into its composite colours. They also compared how light interacts in a variety of optical devices such as kaleidoscopes, periscopes, telescopes and magnifying glasses. At the high school level, students may enrol in physics where they will learn about the wave and particle models of light. In addition, they would be provided with opportunities that would enable them to explain, qualitatively and quantitatively, the phenomena of wave interference, diffraction, reflection, refraction and the Doppler-Fizeau effect. 100 GRADE 8 SCIENCE CURRICULUM GUIDE

3 Curriculum Outcomes STSE Skills Knowledge Students will be expected to Students will be expected to Students will be expected to Nature of Science and Technology describe how technologies develop as a systematic trial-and-error process that is constrained by the properties of materials and the laws of nature relate personal activities in formal and informal settings to specific science disciplines explain the importance of choosing words that are scientifically or technologically appropriate provide examples of ideas and theories used in the past to explain natural phenomena Relationships Between Science and Technology provide examples of scientific knowledge that have resulted in the development of technologies provide examples of technologies that have enabled scientific research Social and Environmental Contexts of Science and Technology provide examples to illustrate that scientific and technological activities take place in a variety of individual or group settings describe possible positive and negative effects of a particular scientific or technological development, and explain how different groups in society may have different needs and desires in relation to it Initiating and Planning identify questions to investigate arising from practical problems and issues define and delimit questions and problems to facilitate investigation state a prediction and a hypothesis based on background information or an observed pattern of events design an experiment and identify major variables formulate operational definitions of major variables and other aspects of their investigations select appropriate methods and tools for collecting data and information and for solving problems Performing and Recording estimate measurements use instruments effectively and accurately for collecting data use tools and apparatus safely Analyzing and Interpreting interpret patterns and trends in data, and infer and explain relationships among the variables state a conclusion, based on experimental data, and explain how evidence gathered supports or refutes an initial idea identify new questions and problems that arise from what was learned Communication and Teamwork receive, understand, and act on the ideas of others identify and describe properties of visible light describe the laws of reflection of visible light and their applications in everyday life describe qualitatively how visible light is refracted describe different types of electromagnetic radiation, including infrared, ultraviolet, X-rays, microwaves, and radio waves compare properties of visible light to the properties of other types of electromagnetic radiation, including infrared, ultraviolet, X-rays, microwaves, and radio waves GRADE 8 SCIENCE CURRICULUM GUIDE 101

4 The Nature of Science - The History of Light Outcomes Students will be expected to provide examples of ideas and theories of light used in the past to explain observed properties. (110-1) Include: (i) Pythagoras belief that light consisted of beams of particles (ii) Galileo s experiment trying to determine the speed of light (iii) Michelson s experiment to measure the speed of light - define light as a form of energy that can be detected by the human eye Elaborations Strategies for Learning and Teaching This unit could begin with a K-W-L activity (Appendix B). By posing motivating questions about light and some of its properties, students conceptions could be assessed and used in the further development of lessons. Student discussion could focus on sources of light, what light is, how it travel, and how fast it travels. Students will have already encountered the term visible light in their study of radiation in the grade 7 Heat unit. Teachers could use the following questions as guides to generate student discussion: What are some things that produce light? Can light be produced in different ways? (While students are not expected to know all of the terms, answers could include: Natural bioluminescence, stars, sun, moon Electric incandescent light bulbs, flashlights and electroluminescence (LED) Chemical chemoluminescence (glow sticks), fluorescence (fluorescent light bulbs) and phosphorescence (glow in the dark materials) Combustion-based candles, fire, torches Nuclear What is light made of, waves, or particles? How does light travel? Does it need something to travel through? If so, what is this something in empty space? How fast does light travel? Is it slower or faster than sound? Students should know that Michelson s experiment was conducted for the purpose of calculating the speed of light. Students do not need to know the details of the experiment. 102 GRADE 8 SCIENCE CURRICULUM GUIDE

5 The Nature of Science - The History of Light Suggested Assessment Strategies Journal The things I know about light are... (can include sources, what it is, how it travels, how fast it travels?) (110-1) Paper and Pencil Resources documents/science/index.html ST pp TR TR AC 24 Conduct research on Pythagoras beliefs about light. (110-1) As an enrichment project, conduct research on Michelson s experiment that measured the speed of light. (110-1) Conventions used in Resources Column ST = Student Text TR = Teacher Resource TR AC = Assessment Checklist TR PS = Process Skills Rubric TR AR = Assessment Rubric BLM = Black Line Master BLM 8 Activity # = Additional BLMs for each grade level GRADE 8 SCIENCE CURRICULUM GUIDE 103

6 The Nature of Science - The History of Light (continued) Outcomes Students will be expected to provide examples of ideas and theories of light used in the past to explain observed properties (110-1) (continued) - identify the speed of light as m/s, or 3 x 10 8 m/s - qualitatively compare the speed of light to the speed of sound Elaborations Strategies for Learning and Teaching Students may initially have difficulty recognizing that light has a speed given that it appears instantaneously. The previous questions and ensuing discussion, would set the stage for introductory, exploratory activities. Teachers could ask students to compare the speed of light to the speed of sound (~ 330 m/s at sea level) using thunder and lightning as an example. The point to stress is that light travels extremely fast; so fast that we cannot notice the time required for it to travel normal distances around us. While sound travels fast (about 1200 km/h), light travels much, much faster ( km/s, or about km/h). In the case of thunder and lightning, the light from a distant lightning strike reaches us (almost) instantly, but the sound from the lightning strike (the thunder) takes longer to reach us. The greater the time delay between seeing the lightning flash and hearing the thunder, the greater the distance between you and the lightning strike. As a rule of thumb, every 3 seconds of time delay equals approximately 1 km of distance. Teachers could challenge students to relate the concepts of time and light by asking the question, How is looking at light coming from stars really like looking at the past? While a star may no longer exist, its light is still traveling towards us because it was so far away from us. provide examples of how scientific knowledge of light resulted in the development of early technologies. (111-1) Include: (i) microscope (ii) telescope Teachers could ask students to generate a list of technologies that are based on the properties of light. This list could include microscopes, telescopes, periscopes, binoculars, fiber optics, cameras, prescription contact lenses, lasers, movie projectors, overhead projectors, etc. Teachers should limit their discussion to the functions of these devices at this point since a more detailed discussion of how the microscope and telescope work will be covered later in this unit and in the grade 9 Space unit. 104 GRADE 8 SCIENCE CURRICULUM GUIDE

7 The Nature of Science - The History of Light (continued) Suggested Assessment Strategies Presentation Resources documents/science/index.html Conduct research on how the microscope or telescope was developed and present to class. (111-1) Performance Create a time line that shows the history of the development of the microscope or telescope. (111-1) Create a collage to show the development of the telescope or microscope. (111-1) ST pp ,149 ST pp , GRADE 8 SCIENCE CURRICULUM GUIDE 105

8 Properties of Visible Light Outcomes Students will be expected to identify and describe properties of visible light. (308-8) Include the following properties, definitions and examples: (i) travels in a straight line (rectilinear propagation) e.g. shadow formation (ii) reflects (reflection) e.g. mirrors (specular) and dust (diffuse) (iii) refracts (refraction) e.g. bent stick effect (iv) disperses (dispersion) e.g. formation of a rainbow as light separates into its constituent colours (v) travels through a vacuum (does not require a medium) e.g. light from Sun and stars reaching Earth through space (vi) travels through transparent, translucent and opaque materials to different amounts e.g. window pane, frosted window, and door Elaborations Strategies for Learning and Teaching Teachers could use the demonstrations listed below to introduce the properties of light. Teachers should note that many of these properties will be explored in greater detail later in the unit. 1. rectilinear propagation: hold your hand in front of a beam of light from an overhead projector. Note the sharp details of the shadow of your hand (i.e. ring, knuckles, etc). 2. reflection: place a hand held mirror in the beam of light. Shine the reflected beam from the mirror on the back or side wall. 3. refraction: fill a large beaker or aquarium with water and place a popsicle or stir stick in the beaker. Observe from the side. 4. dispersion: shine a beam of light from a ray box through a prism to observe its constituent colours. 5. travels through a vacuum: use a clear light bulb. The light from the tungsten wire filament travels through the (almost complete) vacuum inside the bulb. The vacuum is evidenced by the pop the bulb makes when it is broken. 6. travels through materials to different amounts: hold a beaker or glass in the beam of an overhead projector. Compare this to the amount of light that passes through a pair of sunglasses, a pane of frosted glass, and a door. Teachers could highlight how the property may or may not be unique to light. For example, light undergoes rectilinear propagation (it does not bend around corners), while sound does not (it can easily bend around corners). However, both light and sound reflect. Students have already explored refraction in elementary science. In grade 7, students learned about the various types of electromagnetic waves and that they do not require a medium in which to travel. Infrared radiation is one type of wave that falls under the category of electromagnetic waves. Teachers could refer to the Heat unit covered in Science 7 where students would have discussed thermographs which make use of infrared waves. Also, students would have learned about heat transfer by radiation, which does not require a medium. By making this link, teachers can help students use their prior knowledge to more easily understand the concepts being covered here. After the terminology has been introduced and various demonstrations have been conducted, teachers could use a Quiz- Quiz-Trade activity (Appendix B) to provide students with an opportunity to practice and use these terms. 106 GRADE 8 SCIENCE CURRICULUM GUIDE

9 Properties of Visible Light Suggested Assessment Strategies Presentation Create a game that includes the properties of light. (308-8) Create a poster or slide show that describes the properties of visible light. (308-8) Paper and Pencil Describe how a beam of light from a ray box appears and acts when it strikes or passes through air filled with chalk dust or smoke (dispersion), mirrors (reflection), and a prism (refraction). (308-8) Create a table of the properties of light and fill in examples of each. (308-8) Resources documents/science/index.html ST pp. 142, , 157, (i) p. 175 (ii) pp. 152, (iii) pp , (iv) pp (v) pp. 142, 157 (vi) pp BLM 2-20, 2-21 TR Performance Create and perform a song or skit that describes the properties of visible light. (308-8) Create a foldable that describes the properties of visible light. (308-8) Create a collage of everyday transparent, translucent and opaque materials indicating which is which. (308-8) GRADE 8 SCIENCE CURRICULUM GUIDE 107

10 Properties of Visible Light (continued) Outcomes Students will be expected to identify and describe properties of visible light (308-8) (continued) - use a prism to observe the dispersion of light - define the visible light spectrum Elaborations Strategies for Learning and Teaching Teachers should refer to the discussion on dispersion at the beginning of this unit. Students will have some experience with the constituent colours of white light. Reference can be made to rainbows that sometimes form in the sky, or the much smaller one that may appear with the use of a sprinkler on a lawn. Sun catchers often take advantage of this property to create some interesting effects. The addition of primary colours to create other colours will likely have been a topic students covered during art class. Reference can be made to such previously acquired knowledge. Teachers should have students use prisms to investigate how light from different sources is refracted and dispersed. Teachers could have students observe and experience what happens to light that is dispersed in a mixture of water and a few drops of milk. Teachers could use a laser to illustrate the point that white light is made from a combination of colours. When white light (e.g. from a ray box or flashlight) is shone through a prism, a spectrum of colours is produced. When a laser light is shone through the prism, the light is refracted (bent) but not dispersed. No other colours are produced because a laser light is one colour only (i.e. is composed of only one wavelength of light). - list the constituent colours of white light, in order of degree of refraction Teachers could provide students with the acronym ROY G BIV to help them remember the order of light wavelengths that make up white light based on smallest refraction (Red) to greatest refraction (violet). 108 GRADE 8 SCIENCE CURRICULUM GUIDE

11 Properties of Visible Light (continued) Suggested Assessment Strategies Performance Create a poster or collage to demonstrate your understanding of the visible light spectrum. (308-8) Create a mnemonic device or acronym to help someone remember the constituent colours of white light in order of degree of refraction. (308-8) Resources documents/science/index.html ST pp TR Journal What questions come to mind when you hear the term visible light? (308-8) ST pp BLM 2-13, 2-14, 2-15 GRADE 8 SCIENCE CURRICULUM GUIDE 109

12 Electromagnetic Radiation and Dispersion Outcomes Students will be expected to recognize the importance of using the words frequency and wavelength correctly (109-13) - define frequency - define wavelength Elaborations Strategies for Learning and Teaching Students will have encountered the term wave in a number of different contexts. Teachers could help students draw comparisons between the various definitions or understandings they have for the term wave. For example, a hand wave represents a repetitive motion of the hand. A wave through a crowd at a sporting event is represented by a repetitive motion of the crowd, as the individuals stand and sit at a regular interval (the rate at which they stand and sit would be the frequency; frequency being the number of repetitions divided by the time). A water wave is represented by a regular upward and downward motion of water particles. A common misconception of students is to believe that the particles in a wave travel forward with the energy transfer. However, this is not the case. The wave through a crowd at a sporting event would be a good way to illustrate this point. As the people stand and sit the wave moves across the stadium but the people themselves do not move from one seat to another. Another way to illustrate this point is to attach a piece of tape onto a spring or rope, and create a wave by moving the spring or rope back and forth. As the wave moves away from your hand the tape simply moves back and forth. A basic introduction into wave theory would be appropriate at this level. Students may have investigated the characteristics of ocean waves which they could then compare to light waves. The use of oscillating ropes and/or slinkies would enable students to have a visual representation of some of the key features of waves such as wave speed, wavelength and frequency. While the term wavelength will likely be new for many students, they should be familiar with the term frequency. Students may have encountered this term previously, especially in mathematics. For example, what is the frequency at which you wash your hair? How frequently do you go to the dentist for check ups? Teachers could use these examples of the common use of the word frequency to build on students prior knowledge and to lead them to an understanding of the term frequency as it applies to wave travel (i.e. how many waves pass a point in a second). Some students may also be able to relate wavelength to different ocean conditions. For example, a rolling sea would have a long wavelength; that is a sea where the boat slowly moves from one peak (crest) to a low point (trough) and then to another peak. However, a choppy sea would have a shorter wavelength. 110 GRADE 8 SCIENCE CURRICULUM GUIDE

13 Electromagnetic Radiation and Dispersion Suggested Assessment Strategies Performance Create a song, poem or rap that explains the difference between frequency and wavelength. (109-13, 308-8) Write a letter to a friend explaining the difference between frequency and wavelength. (109-13, 308-8) Create a story book or comic strip that explains the difference between frequency and wavelength. (109-13, 308-8) Resources documents/science/index.html ST pp BLM 2-9, 2-10 Journal Describe the cues you use to remember the difference between frequency and wavelength. (109-13, 308-8) ST pp GRADE 8 SCIENCE CURRICULUM GUIDE 111

14 Electromagnetic Radiation and Dispersion (continued) Outcomes Students will be expected to recognize the importance of using the words frequency and wavelength correctly (109-13) (continued) - describe the relationship between frequency and wavelength. Include: (i) high frequency waves have short wavelengths (ii) low frequency waves have long wavelengths Elaborations Strategies for Learning and Teaching Teachers could use a 3-4 metre piece of rope attached to a fixed point at one end to model the characteristics of waves: amplitude, wavelength, and frequency. It should be noted that amplitude is not a characteristic we use to distinguish between the different types of waves in the electromagnetic spectrum. However, students will likely identify it as a wave characteristic. By changing one of these characteristics, students can observe and note how the others change. This would be a qualitative exploration and appreciation of the differences and similarities of the different types of electromagnetic radiation. As a point of interest, teachers could inform students that electromagnetic radiation is often labeled based on either its wavelength or frequency. For example, radio stations are often identified by their frequency (OZ FM has a frequency of 94.7 MHz on the Avalon Peninsula, and 95.9 MHz in central Newfoundland.) Radio dials allow you to tune to the specific frequency of this electromagnetic radiation. The radiation used by many cordless phones has a frequency of 2.4 GHz, and is also called microwave radiation. 112 GRADE 8 SCIENCE CURRICULUM GUIDE

15 Electromagnetic Radiation and Dispersion (continued) Suggested Assessment Strategies Performance Create the cartoon characters Wavelength, Frequency, and Energy. Describe the land, Electromagnetic Spectrum, in which they reside. Show how some powers can vary in different parts of the land. (109-13, ) Resources documents/science/index.html ST pp. 140, BLM 2-11 GRADE 8 SCIENCE CURRICULUM GUIDE 113

16 Electromagnetic Radiation and Dispersion (continued) Outcomes Students will be expected to recognize the importance of using the words frequency and wavelength correctly (109-13) (continued) - relate the amount of refraction for each colour to its wavelength. Include: (i) red (longest wavelength - least refraction) (ii) violet (shortest wavelength - greatest refraction) Elaborations Strategies for Learning and Teaching Students should recognize the relationship between wavelength and the colours we see. At this level, discussion should be limited to the fact that all wavelengths of the electromagnetic spectrum enter our eyes. However, our brain can only recognize those with wavelengths in the visible spectrum (i.e. ROY G BIV) and this is limited by the physical make up of our eye. It is important to note that the waves in the visible spectrum comprise only one category of the entire electromagnetic spectrum. Students should realize that white light, when refracted by a prism, illustrates the different wavelengths of visible electromagnetic radiation. The spectrum is often indicated as a continuum of colours with the shortest waves being at the violet end and the longest at the red end. Teachers could have students investigate the colour combinations when the three primary colours of light (red, green and blue) are mixed (Note: the primary colours of light are different from the primary colours used in art: red, yellow, and blue). Teachers could ask students why some objects have a red colour, while others are blue, and still others are white. This could be brought back to the wavelengths of light and that when light strikes an object it is either absorbed or reflected. We only see the wavelengths that are reflected. Thus, a green object is absorbing all the other wavelengths of light and reflecting the wavelength that our brain interprets as green. 114 GRADE 8 SCIENCE CURRICULUM GUIDE

17 Electromagnetic Radiation and Dispersion (continued) Suggested Assessment Strategies Resources documents/science/index.html ST pp BLM 2-12, 2-13, 2-14, 2-15 GRADE 8 SCIENCE CURRICULUM GUIDE 115

18 The Electromagnetic Spectrum Outcomes Students will be expected to describe the different types of electromagnetic radiation and compare properties to visible light (308-11, ) - describe the electromagnetic spectrum in terms of wavelength, frequency, and energy. Include, in order of decreasing wavelength: (i) radio waves (ii) microwaves (iii) infrared (iv) visible light (v) ultraviolet (vi) x-rays (vii) gamma rays Elaborations Strategies for Learning and Teaching Students may struggle with the prevalence of the various types of electromagnetic radiation. This may be natural, given that the information we take in visually plays such a significant role in our lives; hence, visible light might be considered to be a significant portion of the electromagnetic spectrum. To help students realize the magnitude of the other components of the electromagnetic spectrum, teachers could ask students, As you sit in your chair, what devices could you use to receive or send information that do not avail of visible light? In the response, devices such as radios, cell phones, television remote controls, television signals (not through wire), wireless internet connections, might just be a few such devices identified. Teachers should ensure that students realize that all of this radiation is continuously present, however, we do not detect it because its wavelength is either too short (eg; ultraviolet) or too long (eg; infrared). We only continually detect visible light with our eyes. Teachers should compare the wavelength, frequency, and energy in relation to the visible spectrum for the other categories that comprise the electromagnetic spectrum. For example, radio waves have a longer wavelength, lower frequency, and lower energy in comparison to the visible spectrum. Students will have heard of various forms of electromagnetic radiation, such as microwaves and radio waves, but will not necessarily know that there is a connection among them. Teachers could use a learning strategy such as Think-Pair-Share or Numbered Heads (Appendix B) to help illustrate the relationship among the various forms of electromagnetic radiation, their similarities and differences. - provide examples of the use of each type of electromagnetic radiation. Include: (i) radio waves: telecommunications (ii) microwaves: cooking food (iii) infrared: motion sensors (iv) visible light: microscope (v) ultraviolet: sun tanning (vi) x-rays: medical detection (vii) gamma rays: radiation therapy for cancer Teachers could have students investigate the various uses of electromagnetic radiation and identify problems or issues related to particular kinds. Ultraviolet radiation (UVA rays) getting through the atmosphere and storage of radioactive materials are but two of many that could be addressed in this section. 116 GRADE 8 SCIENCE CURRICULUM GUIDE

19 The Electromagnetic Spectrum Suggested Assessment Strategies Performance Create a poster or slide show of the electromagnetic spectrum showing the wavelength, frequency, and energy of the various types of radiation (308-12) Resources documents/science/index.html ST pp TR BLM 2-3 ST pp ST pp , , (i) p. 158 (ii) p. 159 (iii) p. 161 (iv) pp (v) pp (vi) pp (vii) p. 164 GRADE 8 SCIENCE CURRICULUM GUIDE 117

20 The Electromagnetic Spectrum (continued) Outcomes Elaborations Strategies for Learning and Teaching Students will be expected to describe possible negative and positive effects of technologies associated with electromagnetic radiation (113-2) - recognize that generally, higher energy radiation is more harmful to humans identify new questions and problems that arise from what was learned about electromagnetic radiation. (210-16) Teachers should ensure that students have an opportunity to investigate common technologies that incorporate the use of electromagnetic radiation and describe their possible positive and negative effects. Microwave ovens, x-ray machines, cellular phones, and the nuclear industry are some examples of technologies that could be explored. Radio waves have photons with low energies. Microwaves have a little more energy than radio waves. Infrared has still more energy than visible light, ultraviolet, X-rays and gamma-rays. Teachers are not expected to discuss the term photons but simply present the general order of energies. Teachers could use the following table to help students: Electromagnetic Radiation Radio Waves X-rays Ultraviolet Gamma Rays Positive Effects improved telecommunications medical detection used to treat jaundice in babies radiation therapy for cancer Negative Effects uncertain of long-term exposure effects over exposure can lead to cancer skin cancer can kill exposed cells Exposure to high frequency, short wavelength electromagnetic radiation, such as gamma rays, is generally more dangerous. Exposure to low frequency, long wavelength electromagnetic radiation, such as radio waves, is generally less dangerous. As a result, colloquially, high frequency waves are sometimes referred to as high energy waves and low frequency waves are sometimes referred to as low energy waves. Teachers could involve students in a discussion of how the unique characteristics of Earth s atmosphere make Earth a habitable planet for humans. Earth s atmosphere is able to protect us from some of the more dangerous electromagnetic radiation present in space, making Earth a safe place for humans. Living in space or on another planet would expose humans to much more electromagnetic radiation. As discussed in grade 7 Science, humans are adapted to Earth s conditions. Changes to these conditions could compromise our safety. 118 GRADE 8 SCIENCE CURRICULUM GUIDE

21 The Electromagnetic Spectrum (continued) Suggested Assessment Strategies Performance Create a collage of pictures showing the uses of various forms of electromagnetic radiation. (113-2) Create a safety pamphlet highlighting the dangers associated with exposure to specific types of high energy radiations and how to avoid these energies (e.g. UV, x-ray, gamma). (113-2) Resources documents/science/index.html ST pp GRADE 8 SCIENCE CURRICULUM GUIDE 119

22 Reflection Outcomes Students will be expected to formulate operational definitions for incidence, reflection, and the normal (208-7) - define: (i) incident light ray (ii) reflected light ray (iii) normal (iv) angle of incidence (v) angle of reflection (vi) specular reflection (vii) diffuse reflection Elaborations Strategies for Learning and Teaching Teachers could introduce this section by demonstrating specular reflection using a ray box and plane mirror. Teachers could shine two or more rays of light onto a mirror and ask students to look for patterns or similarities in what they observe. Observations could be used to formulate operational definitions for these terms. Teachers could use the flex-camera to help students observe this demonstration. Students could use a tennis ball thrown against the floor at different angles. Using white poster paper / bristol board paper on the wall, the motion of the ball can be mapped as it hits the floor and bounces up. Alternatively, teachers could use an overhead, soft rubber ball and a straight edge piece of wood. Roll the ball at the wood at different angles. Using the images on the board, have students map the motion of the ball. Use several different incident angles. This demonstration could be used as an introduction to drawing simple ray diagrams. Teachers could guide students to formulate their own definitions by drawing a diagram on the board showing the mirror, the incident ray, the reflected ray and the normal. Teachers could then have students propose and discuss their definition for each term. Regardless of the instructional strategy employed, teachers should ensure that students understand that the angles of incidence and reflection are estimated or measured with respect to the normal. Teachers could have students explore and investigate the differences between specular and diffuse reflection by comparing the reflection from smooth and crumpled aluminum foil. Teachers could employ the Two-minute Review strategy (Appendix B) to review these terms. 120 GRADE 8 SCIENCE CURRICULUM GUIDE

23 Reflection Suggested Assessment Strategies Journal Resources documents/science/index.html Imagine you are a science teacher. Summarize what students should know about mirrors and reflections. (209-3, 210-6) Paper and Pencil Produce a simple ray diagram that helps to compare and contrast regular and diffuse reflection. (208-7) ST pp BLM 2-22, 2-25 GRADE 8 SCIENCE CURRICULUM GUIDE 121

24 Reflection (continued) Outcomes Students will be expected to describe the laws of reflection of visible light and their applications in everyday life (308-9) - identify applications of specular and diffuse reflection - list three types of mirrors. Include: (i) plane (ii) concave (iii) convex Elaborations Strategies for Learning and Teaching Teachers should make students aware of applications of specular and diffuse reflection. An example students may be familiar with is the difference between matte and glossy paints. Matte paints have a higher proportion of diffuse reflection resulting in lower luster. Glossy paints have a greater proportion of specular reflection resulting in a shinier appearance. Teachers could show students examples of these paint types to help reinforce the concept. Other examples teachers could refer to include: the different surfaces used for counter tops furniture wax or car wax glazed vs. unglazed ceramics matte vs. glossy finish on photographs Teachers could also show how our knowledge of specular and diffuse reflection has lead to new technologies, such as the science of stealth aircraft. To introduce mirrors and their uses, teachers could use a plane mirror positioned at the front of the class. Ask students, What changes can be a made to the mirror, so that what you see in the mirror is changed? Some alternative sample questions are: How can the mirror s field of view be changed? How can the mirror be changed to produce a larger image? How can the mirror be changed to produce a smaller image? Students may refer to their personal experiences with surveillance mirrors, school-bus mirrors, some vehicle side-view mirrors, and circus or distorting mirrors. Teachers should ensure that students have the opportunity to observe flat, convex and concave mirrors to illustrate the different effects and uses of these types of reflections. - provide examples of each type of mirror. Include: (i) bathroom mirror (plane) (ii) inside of a metal spoon (concave) (iii) safety mirror on the front of a school bus (convex) Students could be challenged to identify additional examples of each type of mirror in their daily lives or to conduct research on the different types. This could include manufactured mirrors (e.g., hand-held personal mirror) or surfaces that behave as mirrors (e.g., outside of metal spoon is a convex mirror). 122 GRADE 8 SCIENCE CURRICULUM GUIDE

25 Reflection (continued) Suggested Assessment Strategies Journal Reflect on where we use mirrors in everyday life and the uses we have for them. (308-9) Performance List examples of everyday objects that use mirrors or other reflective surfaces to view objects at various angles (diffuse reflection). (308-9) Observe objects using the three different types of mirrors. Describe the images you observe and suggest uses for this type of mirror. (210-1) After practicing ray diagrams, in small groups create posters representing the various ray diagrams to be displayed in class. (210-16) Place a mirror in front of a ray box at an angle. Estimate and then measure the angle of incidence and reflection. (208-7, 209-2) Resources documents/science/index.html ST pp ST pp. 188, 197, 204 BLM 2-24, 2-26, 2-27, 2-31 Presentation Create a poster or multimedia presentation to describe and give examples of plane, concave, and convex mirrors. (308-9) Paper and Pencil Why are surveillance mirrors, and side view mirrors on vehicles always convex mirrors? (308-9) ST pp. 191, 196, , , 206 GRADE 8 SCIENCE CURRICULUM GUIDE 123

26 Reflection (continued) Outcomes Students will be expected to use mirrors effectively and accurately for investigating the characteristics of images formed (209-3) define and delimit questions and problems to facilitate investigation (208-3) state a prediction and a hypothesis based on background information or an observed pattern (208-5) use tools and apparatus safely (209-6) state a conclusion, based on experimental data, and explain how evidence gathered supports or refutes an initial idea (210-11) Elaborations Strategies for Learning and Teaching Core Laboratory Activity: Demonstrating the Law of Reflection and Applying the Law of Reflection The laboratory outcomes 208-3, 208-5, 208-7, 209-3, 209-6, and, are addressed, in whole or in part, by completing CORE LAB 5-2B Demonstrating the Law of Reflection and 5-2C Applying the Law or Reflection. Teachers should ensure students know how to measure angles using a protractor. This would include the angle of incidence and the angle of reflection. Students should use a ruler for drawing rays to ensure that they are straight. Teachers should ensure students arrive at the conclusion that the angle of incidence and angle of reflection are equal. Also, through measurements taken, the relationship between object distance and image distance should be observed. Students may ask why the image produced in a plane mirror appears to be behind the mirror even though the object is in front of the mirror. To help students understand, teachers could emphasize the relationship between how the human eye forms an image and how a ray diagram is drawn. That is, the human brain extrapolates the reflected rays from a point on an object to a point where they intersect. The image is formed at this point of intersection, where the brain believes the object to be. Teachers could also discuss lateral inversion (the reversing of an image). This could be demonstrated by holding printed text in front of a plane mirror, and observing that the text is reversed. 124 GRADE 8 SCIENCE CURRICULUM GUIDE

27 Reflection (continued) Suggested Assessment Strategies Resources documents/science/index.html Core Lab # 5: Demonstrating the Law of Reflection and Applying the Law of Reflection ST pp ST pp , 488 (Science Skills) TR TR AR 3, 5 BLM 2-26, 2-27, 2-28 GRADE 8 SCIENCE CURRICULUM GUIDE 125

28 Reflection - Plane Mirrors Outcomes Students will be expected to describe the laws of reflection of visible light and their applications in everyday life (308-9) - recognize that the angle of incidence is equal to the angle of reflection - state the law of reflection - recognize that a ray diagram is a useful way to represent the behavior of light Elaborations Strategies for Learning and Teaching Through the activities of CORE LAB 5-2B and 5-2C, students should be able to explain the relationship between the incident and reflected angles and be able to identify each type. Through these experiences and discussions of reflected beams, teachers should ensure students are able to estimate angles of incidence and reflection. After completion of first part of CORE LAB 5-2B, students should be able to state the law of reflection. Teachers should make students aware that the diagram produced in CORE LAB 5-2C is a simple ray diagram. Teachers should limit discussion of ray diagrams as a means of representing the path of a single beam of light. Students will develop a more complete understanding of ray diagrams in subsequent sections of this unit. Following the core lab activity, teachers should provide students with opportunities to construct ray diagrams showing image formation in a plane mirror. The ray diagrams should clearly illustrate image properties using SPOT (Size, Position, Orientation, Type): The image size is equal to the object size. The image distance is equal to the object distance. The image is upright. The image is virtual. Teachers could extend this topic of plane mirrors to situations including combinations of plane mirrors, such as, three way wardrobes mirrors (360 o mirrors) and fun house mirrors. It is not expected that students would be able to draw ray diagrams to model these situations. use mirrors effectively and accurately for investigating the characteristics of images formed (209-3) - differentiate between real and virtual images Students understanding of the difference between real and virtual images should be limited to the location of the image on a ray diagram. If the image is in front of the mirror (reflected rays converge in front of mirror) the image is real. If the image is behind the mirror (reflected rays are extrapolated and converge behind the mirror) the image is virtual. 126 GRADE 8 SCIENCE CURRICULUM GUIDE

29 Reflection - Plane Mirrors Suggested Assessment Strategies Journal Write a journal entry to show what you have learned about the laws of reflection. (209-2, ) Resources documents/science/index.html ST p. 178 Performance Create and perform a rap that explains the law of reflection. (308-9) ST pp TR TR AC 7 GRADE 8 SCIENCE CURRICULUM GUIDE 127

30 Reflection - Plane Mirrors (continued) Outcomes Students will be expected to use mirrors effectively and accurately for investigating the characteristics of images formed (209-3) (continued) - describe the image properties in plane mirrors. Include: (i) size (ii) position (iii) orientation (iv) type Elaborations Strategies for Learning and Teaching Teachers should ensure students are able to: recognize and label a ray diagram, draw a ray diagram with a given template (see below) explain observations of an image using a ray diagram (use SPOT method: Size, Position, Orientation, and Type). Mirror - construct ray diagrams of images in plane mirrors In a plane mirror: Image size is equal to object size. Image distance is equal to object distance. The image is upright. The image is virtual. Teachers should ensure students have sufficient hands-on practice using mirrors as well as drawing ray diagrams that they are able to locate an image and give a general description (using a ray diagram) when given an object s location. As enrichment, teachers could challenge students to construct a periscope or design and build a classroom surveillance system using a number of small, plane mirrors. Alternatively, students could explore how combinations of mirrors are used in fun house applications to produce different types of images. These types of problem-solving activities would require students to use the laws of reflection in the given context and practice many of the skills-related outcomes. Teachers could have students address these problems in a general sense or in a very detailed manner using ray diagrams to explain these more complex phenomena. Students could work in pairs or in small groups to plan, design and problem-solve. Students could defend their plans/designs/models by presenting their ideas to other groups, to the class as a whole, or by preparing a detailed poster or written report. Teachers could note whether the students share responsibilities for difficulties encountered during the activity as an indicator for the attitudinal outcome on working collaboratively. 128 GRADE 8 SCIENCE CURRICULUM GUIDE

31 Reflection - Plane Mirrors (continued) Suggested Assessment Strategies Paper and Pencil Resources documents/science/index.html Create a diagram to summarize the image characteristics in a plane mirror. (209-3) Performance Write a song that describes the size and orientation of an image in a plane mirror. (209-3) Create a poster that shows the size and orientation of an image in a plane mirror. (209-3) ST pp. 190, 201, 207 Journal Explain to the imaginary friend in the mirror why he or she isn t a real image. (209-3) GRADE 8 SCIENCE CURRICULUM GUIDE 129

32 Reflection - Curved Mirrors Outcomes Students will be expected to use mirrors effectively and accurately for investigating the characteristics of images formed (209-3) (continued) - define focal point - define principal axis Elaborations Strategies for Learning and Teaching Teachers could have students complete investigation 5-3B as a reinforcement of real and virtual images and to introduce concave mirrors. Teachers could have students investigate curved mirror reflection using a ray box and concave mirror. To do this, teachers could have students draw a large T on a piece of paper and place the concave mirror, upright, on the top of the T. Shine a beam of light from the ray box parallel with the T. Place two dots in the middle of the incident and reflected light beams. Remove the ray box and connect the dots. The lines formed will trace the path of the incident and reflected light rays. Repeat this process to obtain at least two more incident ray/reflected ray combinations. Extrapolate each of the reflected rays behind the mirror. Through this activity students should observe a pattern of reflection whereby the point of intersection of these lines identifies the focal point. After such an activity, teachers should lead students to develop operational definitions of focal point and principal axis. - describe how two incident rays reflect on concave mirrors. Include: (i) rays traveling parallel to the principal axis (ii) rays traveling through the focal point Teachers could demonstrate image formation in curved mirrors using large mirrors. Teachers could provide students with handheld mirrors, allowing them to observe the properties of the images formed when they position the mirror differently. Students should be able to recognize that: (i) incident rays parallel to the mirror s principal axis are reflected through the focal point; and (ii) incident rays going through the focal point are reflected parallel to the mirror s principal axis. Knowledge of both properties is necessary for constructing ray diagrams showing image formation. Teachers could use overlapping transparencies and coloured markers to represent each incident and reflected ray. Teachers should provide students with templates which include the principal axis, sketch of mirror, and focal point for all ray diagrams 130 GRADE 8 SCIENCE CURRICULUM GUIDE

33 Reflection - Curved Mirrors Suggested Assessment Strategies Paper and pencil Resources documents/science/index.html Define focal point, focal length, and principal axis. (308-9) Performance Create a song or jingle that explains the differences between focal point and principal axis. (308-9) ST p. 198 ST p. 198 BLM 2-29 GRADE 8 SCIENCE CURRICULUM GUIDE 131

34 Reflection - Curved Mirrors (continued) Outcomes Students will be expected to use mirrors effectively and accurately for investigating the characteristics of images formed (209-3) (continued) - construct ray diagrams showing the formation of images in concave mirrors where the object is at different positions. Include: (i) object between focal point and mirror (ii) object between focal point and two times the focal length (iii) object beyond two times the focal length - use ray diagrams to describe the characteristics of images formed using concave mirrors. Include: (i) size (ii) position (iii) orientation (iv) type Elaborations Strategies for Learning and Teaching Observe the image of an object placed between the focal point and two times the focal point in a concave mirror. Students should observe that the image is inverted and larger than the object. Students will then justify what they observed using a ray diagram. In order to do so, teachers could have students draw a large T on a piece of paper. Place the concave mirror, upright, on the top of the T. Students will place an object (for example, a paper clip) on the principal axis. Shine a beam of light from the ray box parallel with the principal axis such that the beam of light just touches the top of the object. Place two dots in the middle of the incident and reflected light beams. Remove the ray box and connect the dots forming lines that represent the incident and reflected light rays. Identify the focal point. Repeat this process with a beam of light just touching the top of the object in line with the focal point. Place two dots in the middle of the incident and reflected light beams. Remove the ray box and connect the dots forming lines that represent the incident and reflected light rays. Students can now draw the image using the intersection of the two reflected rays. Finally, students can compare the characteristics of the image they have drawn with their initial observations. This procedure can then be repeated with the object between the focal point and the mirror as well as beyond two times the focal length. Note: the textbook illustrates a third ray through the optical centre. This ray is not required to construct an accurate ray diagram. Students should observe that images in concave mirrors vary depending on the object s location. Using SPOT, the following characteristics may be observed: The image is smaller or larger than the object. The image distance is smaller or larger than the object. The image is upright or inverted The image is real or or virtual Note: Students should be able to identify SPOT characteristics from a specific ray diagram but are not expected to memorize them. Students should have opportunities to observe the reflecting patterns of light off concave mirrors. This could be completed prior to introducing ray diagrams for curved mirrors. 132 GRADE 8 SCIENCE CURRICULUM GUIDE